1. Field of the Invention
The present invention relates to a process for recycling printed papers that contain a plastic olefin polymer coating.
The recycling of paper, and especially newspapers today is important for economical and environmental reasons. The printing ink on newspapers has a tendency to come off on the hands, especially while it is fresh, e.g. within the first two or three days. Not only is this messy but it is also dangerous after a prolonged exposure to the printing inks because they contain carbon black which has a number of carcinogens in it, for example benzopyrene and substituted benzopyrenes. The carcinogens are absorbed through the skin when the printing ink gets on the hands. Furthermore, some people are allergic to the printing ink.
Parent patent, U.S. Pat. No. 4,952,426, provides a process for coating paper having printed ink on its surface which comprises applying and adhering a transparent plastic to the paper while the ink is wet. Preferably the paper used is newsprint and the ink used contains carbon black.
When the transparent plastic coated paper of the parent patent contains an olefin polymer as the coating, there are problems in the recycling process since ink will not adhere well to the olefin polymer. Thus, after the deinking step in forming recycled paper and the subsequent printing on recycled paper containing the olefin polymer, printing ink will not adhere well to the olefin polymer portion of the paper which can thus result in unsatisfactory or non-uniform printing.
2. Description of the Related Art
It is known to improve the ability of printing ink to stick to olefin polymers by treating the polymer, eg. in film form, with an oxidizing agent, e.g. ozone, Corona discharge, chromic acid or an oxidizing flame, e.g. see U.S. Pat. No. 2,968,576. It would seem logical to accomplish this by simply adding the additional step of an oxidizing treatment after applying the transparent plastic coating to the paper having printing ink on its surface in the assembly line of forming the final printed paper in the parent patent. However, this has the problem that it prematurely renders the surface of the olefin polymer more susceptible to printing ink so that there will be a greater tendency of the coated paper to retain any ink it comes in contact with in its normal handling and use.
Of at least equal importance, the oxidizing treatment is a surface phenomenon. Consequently even if the surface of the olefin polymer is treated during the preparation of a newspaper, the treatment will not affect the rest of the plastic layer. In the recycling process there will be exposed the interior and bottom portions of the plastic which have not received the oxidizing treatment and consequently will not adhere as well as desired to the ink on the recycled paper which now is composed of not only cellulosic fibers but also fibers resulting from the olefin polymer used as a coating to prevent the ink from getting on the skin and hands of the reader or other handler of the original newspaper.